Vegetative propagation of larch species: somatic embryogenesis improvement towards its integration in breeding programs

Vegetative propagation of forest trees offers advantages to both tree breeders and the forest industry. In larch vegetative propagation has chronologically followed three major developments: (i) clonal propagation by cuttings; (ii) ‘bulk’ vegetative propagation by cuttings and (iii) somatic embryogenesis. The latter has potentially numerous applications such as the production of a large number of genetically improved plants and the amenability of embryogenic cultures to be stored in liquid nitrogen. In Larix sp. several improvements of the somatic embryogenesis protocol have been developed. Maturation conditions are now well enough refined to regenerate high quality somatic embryos that are highly similar to zygotic embryos in their anatomy, physiology and protein content. Among conifer species, somatic embryogenesis of Larix has become a model for its multiple uses; its integration in a breeding program is now undertaken for clonal propagation of improved material of hybrid larch Larix x eurolepis. Indeed, somatic embryogenesis assists breeding strategies by offering an alternative tool for at the same time accelerated production of plants for clonal testing and then for mass production; in addition, cryoconservation allows keeping material in a juvenile state and allows mass production of stored material at any time. This review describes the different methods of vegetative propagation of larch sp., in particular the advances in somatic embryogenesis and requirements for its integration into a breeding program